Duplexer design and implementation for self-interference cancellation in full-duplex communications

The full-duplex (FD) based devices are capable of concurrently transmitting and receiving signals with a single frequency band. However, a severe self-interference (SI) due to the large difference between the power of the devices' own transmission and that of the signal of interest may be imposed on the FD based devices, thus significantly eroding the received signal-to-interference-plus-noise ratio (SINR). To implement the FD devices, the SI power must be sufficiently suppressed to provide a high-enough received SINR for satisfying the decoding requirement. In this paper, the design and implementation of the duplexer for facilitating SI cancellation in FD based devices are investigated, with a new type of duplexer (i.e. an improved directional coupler) designed and verified. It is shown that the SI suppression capability may be up to 36 dB by using the proposed design, which is much higher than that attainable in the commonly designed ferrite circulator.